There is a large body of literature on the actions and activities of IGFs (IGF-I, IGF-II, and IGF variants). Human IGF-I is a 7649-dalton polypeptide with a pI of 8.4 (Rinderknecht and Humbel, Proc. Natl. Acad. Sci. USA, 73: 2365 (1976); Rinderknecht and Humbel, J. Biol. Chem., 253: 2769 (1978)) belonging to a family of somatomedins with insulin-like and mitogenic biological activities that modulate the action of growth hormone (GH). Van Wyk et al., Recent Prog. Horm. Res., 30: 259 (1974); Binoux, Ann. Endocrinol., 41: 157 (1980); Clemmons and Van Wyk, Handbook Exp. Pharmacol., 57: 161 (1981); Baxter, Adv. Clin. Chem., 25: 49 (1986); U.S. Pat. No. 4,988,675; WO 91/03253; WO 93/23071.
Like GH, IGF-I is a potent anabolic protein. See Tanner et al., Acta Endocrinol., 84: 681-696 (1977); Uthne et al., J. Clin. Endocrinol. Metab., 39: 548-554 (1974). See also Ross et al., Intensive Care Med., 19 Suppl. 2: S54-57 (1993), which is a review of the role of insulin, GH, and IGF-I as anabolic agents in the critically ill. IGF-I has hypoglycemic effects similar to those of insulin, but also promotes positive nitrogen balance. Underwood et al., Hormone Res., 24: 166 (1986); Guler et al., N. Engl. J. Med., 317: 137 (1987). Due to this range of activities, IGF-I is being tested in humans for such widely disparate uses as wound healing, treatment of diabetes, reversal of whole body catabolic states, treatment of heart conditions such as congestive heart failure, and treatment of neurological disorders. Guler et al., Proc. Natl. Acad. Sci. USA, 85: 4889-4893 (1988); Duerr et al., J. Clin. Invest., 95: 619-627 (1995); and Science, 264: 772-774 (1994).
U.S. Pat. Nos. 5,273,961; 5,466,670; 5,126,324; 5,187,151; 5,202,119; 5,374,620; 5,106,832; 4,988,675; 5,106,832; 5,068,224; 5,093,317; 5,569,648; and 4,876,242; WO 92/11865; WO 96/01124; WO 91/03253; WO 93/25219; WO 93/08826; and WO 94/16722 disclose various methods of treating mammals, especially human patients, using IGF-I. In addition, clinical uses of IGF-I are described, for example, in Bondy, Ann Intern. Med., 120: 593-601 (1994).
As one specific use, IGF-I has been found to exert a variety of actions in the kidney. Hammerman and Miller, Am. J. Physiol., 265: F1-F14 (1993). It has been recognized for decades that the increase in kidney size observed in patients with acromegaly is accompanied by a significant enhancement of glomerular filtration rate. O'Shea and Layish, J. Am. Soc. Nephrol., 3: 157-161 (1992). U.S. Pat. No. 5,273,961 discloses a method for prophylactic treatment of mammals at risk for acute renal failure. In humans IGF-I has been shown to preserve renal function post-operatively.
Franklin et al., Am. J. Physiol., 272: F257-F259 (1997). Infusion of the peptide in humans with normal renal function increases glomerular filtration rate and renal plasma flow. Guler et al., Acta Endocrinol., 121: 101-106 (1989); Guler et al., Proc. Natl. Acad. Sci. USA, 86: 2868-2872 (1989); Hirschberg et al., Kidney Int., 43: 387-397 (1993); U.S. Pat. No. 5,106,832. Further, humans with moderately reduced renal function respond to short-term (four days) IGF-I administration by increasing their rates of glomerular filtration and renal plasma flow. Hence, IGF-I is a potential therapeutic agent in the setting of chronic renal failure. O'Shea et al., Am. J. Physiol., 264: F917-F922 (1993). Despite the fact that IGF-I can enhance renal function for those experiencing end-stage chronic renal failure, the enhancements of the glomerular filtration rate and renal plasma flow induced by IGF-I short-term do not persist during long-term administration and incidence of side-effects is high. Miller et al., Kidney International, 46: 201-207 (1994).
For complete reviews of the effect of IGF-I on the kidney, see, e.g., Hammerman and Miller, Am. J. Physiol., 265: F1-F14 (1993) and Hammerman and Miller, J. Am. Soc. Nephrol., 5: 1-11 (1994).
As to anabolic indications for IGF-I, in HIV-infected patients treated consecutively with IGF-I, the IGF-I promoted anabolism, but tachyphylaxis developed rapidly in the patients. Lieberman et al., U.S. Endocrine Meeting, June 1993 (Abst. 1664); Lieberman et al., J. Clin. Endo. Metab., 78: 404-410 (1994). In patients with severe head injuries, a condition associated with profound hypercatabolism and nitrogen loss, infusion of IGF-I produced only a transient positive nitrogen balance. In the first week the patients experienced a positive nitrogen balance, but during the second week, a negative nitrogen balance developed. Chen et al., U.S. Endocrine Meeting, June 1993 (Abst. 1596).
IGF-I has hypoglycemic effects in humans similar to those of insulin when administered by intravenous bolus injection.
Underwood et al., Hormone Research, 24: 166 (1986). IGF-I is known to exert glucose-lowering effects in both normal (Guler et al., N. Engl. J. Med., supra) and diabetic individuals (Schoenle et al., Diabetologia, 34: 675-679 (1991); Zenobi et al., J. Clin. Invest., 90: 2234-2241 (1992); Sherwin et al., Hormone Research, 41 (Suppl. 2): 97-101 (1994); Takano et al., Endocrinol. Japan, 37: 309-317 (1990); Guler et al., Acta Paediatr. Scand. (Suppl.), 367: 52-54 (1990)), with a time course described as resembling regular insulin. See also Kerr et al., "Effect of Insulin-like Growth Factor 1 on the responses to and recognition of hypoglycemia," American Diabetes Association (ADA), 52nd Annual Meeting, San Antonio, Tex., Jun. 20-23, 1992, which reported an increased hypoglycemia awareness following recombinant human IGF-I (rhIGF-I) administration. In addition, single administration of rhIGF-I reduces overnight GH levels and insulin requirements in adolescents with IDDM. Cheetham et al., Clin. Endocrinol., 40: 515-555 (1994); Cheetham et al., Diabetologia, 36: 678-681 (1993).
The administration of rhIGF-I to Type II diabetics, as reported by Schalch et al., J. Clin. Metab., 77: 1563-1568 (1993), demonstrated a fall in both serum insulin as well as a paralleled decrease in C peptide levels. This indicated a reduction in pancreatic insulin secretion after five days of IGF-I treatment. This effect has been independently confirmed by Froesch et al., Horm. Res., 42: 66-71 (1994). In vivo studies in normal rats also illustrate that IGF-I infusion inhibits pancreatic insulin release. Fursinn et al., Endocrinology, 135: 2144-2149 (1994). In addition, in pancreas perfusion preparations, IGF-I also suppressed insulin secretion. Leahy et al., Endocrinology, 126: 1593-1598 (1990). Despite these clear in vivo inhibitory effects of IGF-I on insulin secretion in humans and animals, in vitro studies have not yielded such uniform results.
RhIGF-I has the ability to improve insulin sensitivity. For example, rhIGF-I (70 .mu.g/kg bid) improved insulin sensitivity in non-diabetic, insulin-resistant patients with myotonic dystrophy. Vlachopapadopoulou et al.,J. Clin. Endo. Metab., 12: 3715-3723 (1995). Saad et al., Diabetoloaia, 37: Abstract 40 (1994) reported dose-dependent improvements in insulin sensitivity in adults with obesity and impaired glucose tolerance following 15 days of rhIGF-I treatment (25 .mu.g and 100 .mu.g/kg bid). RhIGF-I also improved insulin sensitivity and glycemic control in some patients with severe type A insulin resistance (Schoenle et al., Diabetoloaia, 34: 675-679 (1991); Morrow et al., Diabetes, 42 (Suppl.): 269 (1993) (abstract); Kuzuya et al., Diabetes, 42: 696-705 (1993)) and in other patients with non-insulin dependent diabetes mellitus. Schalch et al., "Short-term metabolic effects of recombinant human insulin-like growth factor I (rhIGF-I) in type II diabetes mellitus", in: Spencer EM, ed., Modern Concepts of Insulin-like Growth Factors New York: Elsevier: 1991) pp. 705-715; Zenobi et al., J. Clin. Invest., 90: 2234-2241 (1993).
A general scheme for the etiology of some clinical phenotypes that give rise to insulin resistance and the possible effects of administration of IGF-I on selected representative subjects is given in several references. See, e.g., Elahi et al., "Hemodynamic and metabolic responses to human insulin-like growth factor-1 (IGF-I) in men," in: Modern Concepts of Insulin-Like Growth Factors, (Spencer, EM, ed.), Elsevier, New York, pp. 219-224 (1991); Quinn et al., New Engl. J. Med., 323: 1425-1426 (1990); Schalch et al., "Short-term metabolic effects of recombinant human insulin-like growth factor 1 (rhIGF-I) in type 11 diabetes mellitus," in: Modern Concepts of Insulin-Like Growth Factors, (Spencer, EM, ed.), Elsevier, New York, pp. 705-714 (1991); Schoenle et al., Diabetologia, 34: 675-679 (1991); Usala et al., N. Eng. J. Med., 327: 853-857 (1992); Lieberman et al., J. Clin. Endo. Metab., 75: 30-36 (1992); Zenobi et al., J. Clin. Invest., 90: 2234-2241 (1992); Zenobi et al., J. Clin. Invest., 89: 1908-1913 (1992); Kerr et al., J. Clin. Invest., 91: 141-147 (1993). When IGF-I was used to treat Type II diabetic patients in the clinic at a dose of 120-160 .mu.g/kg twice daily, the side effects outweighed the benefit of the treatment. Jabri et al., Diabetes, 43: 369-374 (1994). See also Wilton, Acta Paediatr., 383: 137-141 (1992) regarding side effects observed upon treatment of patients with IGF-I.
The IGF binding proteins (IGFBPs) are a family of at least six proteins (Jones and Clemmons, Endocr. Rev., 16: 3-34 (1995); Bach and Rechler, Diabetes Reviews, 3: 38-61 (1995)), with other related proteins also possibly binding the IGFs. The IGFBPs bind IGF-I and IGF-II with varying affinities and specificities. Jones and Clemmons, supra; Bach and Rechler, supra. For example, IGFBP-3 binds IGF-I and IGF-II with a similar affinity, whereas IGFBP-2 and IGFBP-6 bind IGF-II with a much higher affinity than they bind IGF-I. Bach and Rechler, supra; Oh et al., Endocrinology, 132, 1337-1344 (1993).
Unlike most other growth factors, the IGFs are present in high concentrations in the circulation, but only a small fraction of the IGFs is not protein bound. For example, it is generally known that in humans or rodents, less than 1% of the IGFs in blood is in a "free" or unbound form. Juul et al., Clin. Endocrinol., 44: 515-523 (1996); Hizuka et al., Growth Regulation, 1: 51-55 (1991); Hasegawa et al., J. Clin. Endocrinol. Metab., 80: 3284-3286 (1995). The overwhelming majority of the IGFs in blood circulate as part of a non-covalently associated ternary complex composed of IGF-I or IGF-II, IGFBP-3, and a large protein termed the acid-labile subunit (ALS). This complex is composed of equimolar amounts of each of the three components. The ternary complex of an IGF, IGFBP-3, and ALS has a molecular weight of approximately 150,000 daltons, and it has been suggested that the function of this complex in the circulation may be to serve as a reservoir and buffer for IGF-I and IGF-II, preventing rapid changes in free IGF-I or IGF-II.
IGF-I naturally occurs in human body fluids, for example, blood and human cerebral spinal fluid. Although IGF-I is produced in many tissues, most circulating IGF-I is believed to be synthesized in the liver. The IGFBPs are believed to modulate the biological activity of IGF-I (Jones and Clemmons, supra), with IGFBP-1 (Lee et al., Proc. Soc. Exp. Biol. & Med., 204: 4-29 (1993)) being implicated as the primary binding protein involved in glucose metabolism. Baxter, "Physiological roles of IGF binding proteins", in: Spencer (Ed.), Modern Concepts of Insulin-like Growth Factors (Elsevier, New York, 1991), pp. 371-380. IGFBP-1 production by the liver is regulated by nutritional status, with insulin directly suppressing its production. Suikkari et al., J. Clin. Endocrinol. Metab., 66: 266-272 (1988).
The function of IGFBP-1 in vivo is poorly understood. The administration of purified human IGFBP-1 to rats has been shown to cause an acute, but small, increase in blood glucose. Lewitt et al., Endocrinology, 129: 2254-2256 (1991). The regulation of IGFBP-1 is somewhat better understood. It has been proposed (Lewitt and Baxter, Mol. Cell Endocrinology, 79: 147-152 (1991)) that when blood glucose rises and insulin is secreted, IGFBP-1 is suppressed, allowing a slow increase in "free" IGF-I levels that might assist insulin action on glucose transport. Such a scenario places the function of IGFBP-1 as a direct regulator of blood glucose.
The IGF system is also composed of membrane-bound receptors for IGF-I, IGF-II, and insulin. The Type 1 IGF receptor is closely related to the insulin receptor in structure and shares some of its signaling pathways. Jones and Clemmons, supra. The IGF-II receptor is a clearance receptor that appears not to transmit an intracellular signal. Jones and Clemmons, supra. Since IGF-I and IGF-II bind to the Type 1 IGF-I receptor with a much higher affinity than to the insulin receptor, it is most likely that most of the effects of IGF-I and IGF-II are mediated by the Type 1 IGF receptor. Ballard et al., "Does IGF-I ever act through the insulin receptor", in Baxter et al. (Eds.), The Insulin-Like Growth Factors and Their Regulatory Proteins, (Amsterdam: Elsevier, 1994), pp. 131-138.
There has been much work identifying the domains on IGF-I and IGF-II that bind to the IGFBPs. Bayne et al., J. Biol. Chem., 265: 15648-15652 (1990); U.S. Pat. Nos. 5,077,276; 5,164,370; 5,470,828. For example, it has been discovered that the N-terminal region of IGF-I and IGF-II is critical for binding to the IGFBPs. U.S. Pat. Nos. 5,077,276; 5,164,370; 5,470,828. Thus, the natural IGF-I variant, designated des(1-3)IGF-I, binds poorly to IGFBPs.
A similar amount of research has been devoted to identifying the domains on IGF-I and IGF-II that bind to the Type 1 IGF receptor. Bayne et al., supra; Oh et al., supra. It was found that the tyrosine residues in IGF-I at positions 24, 31, and 60 are crucial to the binding of IGF-I to the Type 1 IGF receptor. Bayne et al., supra. Mutant IGF-I molecules where one or more of these tyrosine residues are substituted showed progressively reduced binding to Type 1 IGF receptors. Bayne et al., supra, also investigated whether such mutants of IGF-I could bind to the Type 1 IGF receptor and to the IGFBPs. They found that quite different residues on IGF-I and IGF-II are used to bind to the IGFBPs from those used to bind to the Type 1 IGF receptor. It is therefore possible to produce IGF variants that show reduced binding to the IGFBPs, but, because they bind well to the Type 1 IGF receptor, show maintained activity in in vitro activity assays.
Also reported was an IGF variant that binds to IGFBPs but not to IGF receptors and therefore shows reduced activity in in vitro activity assays. Bar et al., Endocrinology, 127: 3243-3245 (1990). In this variant, designated (1-27,gly.sup.4,38-70)-hIGF-I, residues 28-37 of the C region of human IGF-I are replaced by a four-residue glycine bridge. Bar et al. studied the transport of the mutant IGF-I when it was perfused as a complex with IGFBP through the heart in terms of the localization of IGFBPs bound to the mutant IGF or to IGF itself. There were no data supplied by Bar et al. on the localization of the IGF mutant given alone, only data on the localization of the complex of the IGF mutant and IGFBP. Further, Bar et al. provided no data on any biological or efficacy response to the administration of the IGF mutant.
Other truncated IGF-I variants are disclosed. For example, in the patent literature, WO 96/33216 describes a truncated variant having residues 1-69 of authentic IGF-I. EP 742,228 discloses two-chain IGF-I superagonists which are derivatives of the naturally occurring single-chain IGF-I having an abbreviated C domain. The IGF-I analogs are of the formula: EQU BC.sup.n,A
wherein B is the B domain of IGF-I or a functional analog thereof, C is the C domain of IGF-I or a functional analog thereof, n is the number of amino acids in the C domain and is from about 6 to about 12, and A is the A domain of IGF-I or a functional analog thereof.
Additionally, Cascieri et al., Biochemistry, 27: 3229-3233 (1988) discloses four mutants of IGF-I, three of which have reduced affinity to the Type 1 IGF receptor. These mutants are: (Phe.sup.23,Phe.sup.24,Tyr.sup.25)IGF-I (which is equipotent to human IGF-I in its affinity to the Types 1 and 2 IGF and insulin receptors), (Leu.sup.24)IGF-I and (Ser.sup.24)IGF-I (which have a lower affinity than IGF-I to the human placental Type 1 IGF receptor, the placental insulin receptor, and the Type 1 IGF receptor of rat and mouse cells), and desoctapeptide (Leu.sup.24)IGF-I (in which the loss of aromaticity at position 24 is combined with the deletion of the carboxyl-terminal D region of hIGF-I, which has lower affinity than (Leu.sup.24)IGF-I for the Type 1 receptor and higher affinity for the insulin receptor). These four mutants have normal affinities for human serum binding proteins.
Bayne et al., J. Biol. Chem., 263: 6233-6239 (1988) discloses four structural analogs of human IGF-I: a B-chain mutant in which the first 16 amino acids of IGF-I were replaced with the first 17 amino acids of the B-chain of insulin, (Gln.sup.3,Ala.sup.4)IGF-I, (Tyr.sup.15,Leu.sup.16)IGF-I, and (Gln.sup.3,Ala.sup.4,Tyr.sub.15,Leu.sup.16)IGF-I. These studies identify some of the domains of IGF-I that are responsible for maintaining high-affinity binding with the serum binding protein and the Type 2 IGF receptor.
Bayne et al., J. Biol. Chem., 264: 11004-11008 (1988) discloses three structural analogs of IGF-I: (1-62)IGF-I, which lacks the carboxyl-terminal 8-amino-acid D region of IGF-I; (1-27,Gly.sup.4,38-70)IGF-I, in which residues 28-37 of the C region of IGF-I are replaced by a four-residue glycine bridge; and (1-27,Gly.sup.4,38-62)IGF-I, with a C region glycine replacement and a D region deletion. Peterkofsky et al., Endocrinology, 128: 1769-1779 (1991) discloses data using the Gly.sup.4 mutant of Bayne et al., supra (Vol. 264). U.S. Pat. No. 5,714,460 refers to using IGF-I or a compound that increases the active concentration of IGF-I to treat neural damage.
Cascieri et al., J. Biol. Chem., 264: 2199-2202 (1989) discloses three IGF-I analogs in which specific residues in the A region of IGF-I are replaced with the corresponding residues in the A chain of insulin. The analogs are: (Ile.sup.41,Glu.sup.45,Gln.sup.46,Thr.sup.49,Ser.sup.50,Ile.sup.51, Ser.sup.53,Tyr.sup.55,Gln.sup.56) IGF-I, an A chain mutant in which residue 41 is changed from threonine to isoleucine and residues 42-56 of the A region are replaced; (Thr.sup.49, Ser.sup.50, Ile.sup.51) IGF-I; and (Tyr.sup.55,Gln.sup.56) IGF-I.
Clemmons et al., J. Biol. Chem., 265: 12210-12216 (1990) discloses use of IGF-I analogs that have reduced binding affinity for either the Type 1 IGF receptor or binding proteins to study the ligand specificity of IGFBP-1 and the role of IGFBP-1 in modulating the biological activity of IGF-I.
WO 94/04569 discloses a specific binding molecule, other than a natural IGFBP, that is capable of binding to IGF-I and can enhance the biological activity of IGF-I.
U.S. Pat. Nos. 5,593,844 and 5,210,017 disclose a ligand-mediated immunofunctional binding protein assay method that can be used to quantitate the amount of GH binding protein or IGFBP in a liquid sample by the use of antibodies, where complex formation takes place between one of these binding proteins and the hormone ligand that binds to it.
The direction of research into IGF variants has mostly been to make IGF variants that do not bind to the IGFBPs but show maintained binding to the IGF receptor. The idea behind the study of such molecules is that the major actions of the IGFBPs are proposed to be an inhibition of the activity of the IGFs. Chief among these variants is the natural molecule, des(1-3)IGF-I, which shows selectively reduced affinity for some of the IGF binding proteins, yet a maintained affinity for the IGF receptor. U.S. Pat. Nos. 5,077,276; 5,164,370; 5,470,828, supra.
There is a need in the art for a molecule that acts as an IGF agonist, and also for a molecule that binds to IGF binding proteins with high affinity and specificity for therapeutic or diagnostic purposes.